In round 4, we observed:
- highest prevalence in 18 to 24 age group at 0.25% (0.16%, 0.41%), increasing from 0.08% (0.04%, 0.18%) in round 3.
- lowest prevalence in 65+ at 0.04% (0.02%, 0.06%)

Participants of Asian ethnicity had elevated odds of infection.

We identified clusters in and around London, transient clusters in the Midlands, and an expanding area of clustering in the North West and more recently in Yorkshire and the Humber.

Interpretation:
Low levels of transmission persisted in England in mid-summer 2020, but the prevalence of SARS-CoV-2 is now increasing.

We found evidence of accelerating transmission at the end of August and beginning of September 2020.

Studies like REACT-1 (representative community antigen sampling)
- can increase situational awareness
- be used as an early warning system
- be used to rapidly evaluate success of policies in keeping the virus controlled at low prevalence